Halogenated elastomers, chloro and bromo butyl rubbers are widely used in the preparation of mechanical goods and of inner liners of tires. These rubbers are characterized by their excellent chemical resistance, and low gas permeability. A salient drawback of compounds based on these rubbers is their inherent susceptibility to premature vulcanization, i.e. scorching during processing and/or storage. Premature vulcanization causes the compounds to become tough and unworkable. Commonly used cure systems for these elastomers therefore include retarders.
In U.S. Pat. No. 3,865,763 certain boron compounds were disclosed to be effective by retarding the scorch of halogenated butyl rubbers. In U.S. Pat. No. 3,880,821 there were disclosed certain free acids or the magnesium, aluminum, calcium, and barium salts of an oligomer of linoleic acid to be suitable scorch retarding agents in halogenated butyl rubbers. In U.S. Pat. No. 4,128,510 it was disclosed that certain derivatives of 2,5-dimercapto-1,3,4-thiadiazole used in the presence of certain basic materials are suitable in promoting crosslinking without sticking or premature curing of certain saturated and unsaturated halogen containing polymers. These halogen containing polymers include chloro butyl rubber and bromo butyl rubber. U.S. Pat. No. 4,410,704 disclosed N-substituted benzothiazole-2-sulfonamide to be useful in preventing scorching in halogenated butyl rubbers. In U.S. Pat. No. 4,569,958 there were disclosed compounds containing halogenated butyl rubbers which have been rendered scorch resistant upon the addition of a di or tri-thiol-s-triazine compound and at least one carboxylic acid compound. A cure system used in crosslinking halogenated butyl rubbers disclosed in U.S. Pat. No. 4,514,396 uses a thiourea derivative as a crosslinking agent, an inorganic base as an acid exceptor and a thiuran sulfide as an accelerator.
In addition to the above, dibenzothiazyl disulfide (MBTS) tetramethylthiuran disulfide (TMTD) and N-cyclohexylbenzothiazyl-2-sulfenamide (CBS) have been disclosed to be useful as retardants. For instance, in a zinc oxide/sulfur cure system MBTS is often added. This system is not entirely satisfactory, especially for bromo butyl rubbers, because it results in an unfavorable cure rate and a reduction in the level of the mechanical properties after aging.